Method and apparatus for inserting contacts in glass tubes



Oct. 25, 1949. e. N. PHELPS 2,485,769

METHOD AND APPARATUS FOR INSERTING CONTACTS IN GLASS TUBES Filed Dec.29, 1944 6 80! jKPheQ-S Patented Oct. 25, 1949 UNITED STATES PATENTOFFICE METHOD AND APPARATUS FOR INSERTING CONTACTS IN GLASS TUBES GeorgeN. Phelps, Lancaster, Pa., assignor to Radio Corporation of America, acorporation of Delaware 15 Claims. 1

My invention relates to perforating sheet glass and more particularly tomaking a hole in the wall-=01 a glass bulb and sealing a metal disc orbutton contact in the hole.

In some types of cathode ray tubes as, for example, the tube disclosedin U. S. Patent 2,323,- 148. McLaughlin, June 2, 1943, a disc or buttoncontact is sealed into the side wall of the bulb. A conventional methodfor sealing this disc or button contact into the bulb wall is to softena spot on the bulb wall with a pointed flame, blowing out a hole at thesoftened spot about the size of the contact by introducing compressedair into the bulb, inserting the metal disc or contact in theho le, andsealing the edge of the contact to the glass by gas fires. Thisconventional method requires a skilled operator, is comparatively slow,

and the product varies in appearance and quality.

The principal object of my invention is to provide an improved method ofmaking in a sheet of glass, such as the wall of a glass bulb, a cleancut hole of predetermined size which is more suitable for receiving adisc or button contact for sealing into the glass wall than the holemade in the conventional way. Another object is to provide a faster andeasier method of sealing metal discs or button contacts into a glasswall and to make such seals more uniform in appearance and quality thanthose usually obtained by conventional methods. A further object is toprovide an apparatus or fixture to facilitate the practice of myimproved method.

-In accordance with my invention a metal punch preferably having acupped or concave working end is held with its working end incontactwith a sheet of glass as, for example, the inside wall of a glassbulb, and is heated by a high frequency coil until the glass in contactwith the edge'k of the punch becomes soft and plastic. When pressedagainst the glass, the heated punch displaces the softened glassimmediately underneath the edge of the punch, making in the glass acrease or groove which deepens until the punch goes'through the sheet ofglass and leaves in it a clean-cut hole. Good results have been obtainedwith a single turn heating coil somewhat larger in diameter than thedisc or button contact held closeto the glass opposite to and coaxialwith the punch, the field of the coil extending through the sheet ofglass to the punch, which passes through the glass and also through theheating coil when the hole is punched.

The metal disc or button contact, slightly larger than the hole made bythe punch, is sealed into the wall of the bulb in accordance with myinvention by inserting the contact in the hole with its edge resting onand slightly overlapping the edge of the hole, and subjecting it to thehigh frequency field of an induction heating coil so placed that theedge of the disc or button contact is heated by induction toglass-to-metal sealing temperature. The single turn induction heatingcoil heats the edge of the disc or contact button and the adjoiningglass more than the center, so that glass-to-metal sealing temperatureis reached only in an annular zone along the edge of the contact button.

Further, in accordance with my invention, and to facilitate the practiceof my invention, I provide a fixture or jig by means of which the punchmay be held firmly against the inside wall of the bulb at a selectedpoint while it is subjected to the field of the high frequency heatingcoil and the operator may at will exert a controlled pressure upon thehot punch to force it through the wall of the bulb.

My invention will be better understood in connection with theaccompanying drawing in which Fig. l is a view showing partly in sectiona cathode ray bulb and a fixture or jig to facilitate the punching of ahole in the wall of the bulb in accordance with my invention; Figs. 2,3, and 4 are fragmentary views in cross-section showing successive stepsof punching the hole; Fig. 5 is a plan view of the single turn inductioncoil for heating the punch; Fig. 6 is a sectional view of a portion ofthe bulb wall showing the metal disc or contact and the single turninduction heating coil in position for sealing the contact into the bulbwall; and Fig. 7 is a sectional view of the same portion of the bulbwall with the contact sealed to the glass.

In accordance with my invention a hole is punched in a sheet of glassID, for example, the glass wall of the bulb of a cathode ray tube, by aconcave metal punch II, the edge of which is pressed against the sheetof glass at the point where the hole is to be punched. The punch may bemade of any metal which is rigid at the temperature at which glasssoftens, and may be of various forms and sizes. Preferably the workingend which contacts the glass sheet is sufficiently concave to provide anannular cutting edge or rim of the size and shape of the hole to bepunched. The punch Il may be made of nickel about 16 mils thick andshaped as a seamless cup about one-half inch in diameter and aboutone-fourth inch deep with a hole [2 about one-eighth inch in diameter inthe center of the bottom of the cup. Preferably the punch is slightlytapered so that it is of maximum diameter at the working end which makescontact with the sheet of glass during the punching operation.

The concave or cup-shaped punch is held with its edge in contact withthe inner side of the wall IU of the bulb, and is at will pressedagainst the glass by a punch holder l3, which may conveniently be acylinder of refractory insulation with a coaxial smaller pin I4projecting from its end and of such a size that it will fit loosely intothe hole I2 in the bottom of the cup-shaped punch H. The end of thecylinder [3 around the pin l4 forms a shoulder on which the bottom ofthe cup-shaped punch rests. A high frequency induction coil l5 which mayconveniently, though not necessarily, be on the opposite side of thesheet of glass from the punch is so positioned that the working end ofthe punch is in the magnetic field of the coil. The particular heatingcoil shown in the drawing, merely as an example, is a single turn highfrequency coil about 1 inch in diameter and preferably of metal tubingto permit water-cooling. The coil is positioned opposite the punch andcoaxial with it and on the outside of the bulb during the punchingoperation. The field of the single turn coil 15 when it is supplied withhigh frequency current, for example a current of about 500 to 600milliamperes at a frequency of about 600 kilocycles, will quickly heatthe edge of the punch to a temperature at which the glass adjoining theedge of the punch and in contact with it is softened to such an extentthat a comparatively slight pressure on the punch will force it into andthrough the annular zone of softened glass at the edge of the punch,thereby forming a clean-cut hole 16, best shown in Fig. 4, ofsubstantially the same size as the punch. It is found in practice thatthe glass which is punched out to form the hole tends to stick to thepunch and to accumulate in the cavity of the punch as a more or lessadherent mass of glass IT. A convenient way to crack off and dislodgethis mass of glass I! so that the punch can be used again is to drop thehot punch into water in a water pan I8, as indicated in Fig. 4.

In order to avoid localized strains in the glass wall during thepunching operation, contact of the heated glass with the water-cooledhigh frequency coil l5 should be avoided. The bulb may with safety reston an annular support I9 of refractory insulation coaxial with the coill5 and preferably carried on a vertically adjustable pedestal 20. Theupper side of the annular support 19 on which the bulb rests, projectsabove the plane of the coil l5, and when the wall of the bulb rests onthe support [9, with the punch H in place on the inner wall of the bulband coaxial with the water-cooled induction coil and the annularsupport, the wall of the bulb cannot touch the coil.

As shown in Fig. 5, the annular support l9 and the high frequency coill5 may conveniently be formed into a unit by a clamp 2i which engagesthe annular support and also grips the legs of the heating coil by meansof insulating sleeves or in other suitable ways. As indicateddiagrammatically in Fig. 5, the heating coil is connected to anoscillator or high frequency generator 22 which will deliver sufficientcurrent of the desired frequency such as 600 kilocycles to bring theedge of the punch to the desired temperature.

The contact button is preferably sealed into the hole in the side wallof the bulb by means of 4 high frequency induction heating as shown inFigs. 6 and '1. The contact button 23, which may be made of any metalwhich will seal to glass and preferably of some of the known chrome-ironalloys which have a coeflicient of expansion and other propertiessuitable for a good glass-to-metal seal, is placed in the punched outhole l6 where its edge slightly overlaps the edge of the hole. Thesealing-in may be done with the high frequency induction coil l5 byholding the bulb under and close to the coil and coaxial with it, asindicated in Fig. 6, to enable the high frequency field of the coil tobring the edge of the contact button and the adjoining glass to sealingtemperature. In this way the button is heated and sinks into the glassand the adjoining glass is thoroughly melted and forms a bead or ridge24 over the edge of the button so that a gOOd glass-to-metal seal ismade. Sometimes it is advantageous to pull the button outward to aslight extent while the glass of the seal is soft to work the seal tosome extent and also to position the contact button slightly above theouter surface of the bulb wall.

.. The bulb with the sealed-in button contact is then annealed from 1 to2 minutes to a temperature of 375 to 400 C., and then for a similarlength of time at about 300 C. After the bulb cools down it is placed inan oven for the usual annealing treatment for bulbs of this kind.

My method of perforating a sheet of glass bypressing through it a punchheated by induction from a high frequency coil may be carried out invarious ways and the practice of my method may be facilitated by the useof various forms of fixtures or other apparatus. For example, and.merely for purposes of illustration, I have shown in Fig. 1 a fixture orjig which I have found to be useful and convenient in practicing myinvention to make holes in the side wall of a cathode ray bulb. In thisparticular device the punch holder [3 is mounted on the end of aswinging arm 25 pivoted on a pivot 25 on a frame or fixture rod 26 whichacts as a bulb carrier for a bulb placed over it. This particularfixture rod has two parallel side members 21 spaced a distance slightlygreater than the width of the arm. 25 so that the arm can swing betweenthe side members about its pivot through an angle of about between theposition shown in full lines on one side of the rod 26 and the position.25a shown in dotted lines on the other side of the rod. The frame orfixture rod is rotatably mounted in a frame socket 26 having a shoulderor stop 29 in position to be engaged by a projecting pin 30 on thefixture rod. The frame socket is held in a bracket 3] on a base 32, andpreferably is pivoted in the bracket 3| so that the angle of the fixturerod with the base may be varied at will.

Contact of the cathode ray bulb with the metal of the fixture rod orframe 26 is undesirable and to prevent such contact a sleeve 33 ofrefractory insulation and longer than the bulb surrounds the fixturerod, with its end projecting beyond the inner end of the fixture rod sothat when the end face of a bulb on the fixture rests against the end ofthe insulating sleeve 33 the bulb is properly positioned. To permit thearm 25 to swing far enough on both sides of the axis of the fixture rodthe sleeve 33 is provided with dia metrically opposite slots 34 inregistry with the space between the side members 2! or the fixture rod.The arm 25 is swung about its pivot by a connecting rod 35 slidableendwise in 'the frame and actuated by a handle 36, which is pivoted onthe rod 26 and through the connecting rod 35 controls the arm and swingsit between the frame members 21 and through the slots 34 from one sideto the other of the fixture rod. The handle 36 is an actuating means forthe punch holder and also for tuning the rod 26 back and forth in thesocket 28 as indicated by the double pointed arrow A. By manipulatingthe handle 36 the rod 26 may be turned from the position shown in fulllines and the parts mounted on it brought into the dotted line positions25a, a and 36a.

In practicing my invention with the aid of this fixture, the bulbs arepre-heated to about 275 to 300 C. and placed over the fixture rod asshown in Fig. 1. The punch H, heated to about 309 has previously beenplaced on the punch holder I3 which at this time is close to the sleeve34 and is pointing upward because the fixture rod is in the loadingposition 180 from the position shown in full lines. After the bulb is inplace, the handle 36 is moved back and toward the socket 28 into theposition 36a shown in dotted lines, to swing the arm 25 upward, therebyswinging the punch holder with the punch on it into the dotted lineposition 25a where the punch rests lightly on the inner wall of thebulb. The fixture rod turned by means of the handle 36 through an angleof 180 into the position shown in full line: while the punch, pressedlightly against the bulb, slides along the wall of the bulb. This halfturn of the fixture rod 26 brings the handle 35 from the dotted lineposition 36a to the full line position, the pin 3|] on the fixture rodup against the shoulder 29 of the bracket, and places the punch I I justabove the center of the induction or work coil 15, as shown in fulllines. During this half rotation of the fixture rod the bulb isstationary but the punch, kept in place on the holder by a lightpressure exerted on the holder l3 through the handle 36, slides over theinner wall of the bulb until it is centered over the induction coil. Theoscillator or high frequency generator 2! is then energized, the punchis heated by high frequency induction, thereby heatin and softening theglass in contact with the edge of the punch, and is then pressed throughthe side wall of the bulb by light pressure exerted through the handle36, finally going through the coil l5 and dropping off the holder intothe pan of water, where the glass cracks off and the punch is ready forre-use. The pressure exerted on the punch to force it through the sidewall of the bulb can be regulated by the operator. In some cases it hasbeen found that a slight increase in pressure just as the punch goesthrough the wall of the bulb contributes to the formation of a clean-cuthole. After the hole is punched the bulb is quickly removed from thefixture and the area around the hole is heated by a gas flame to relieveany strains set up by the punching operation. This heating should bedone within four or five seconds after the hole is punched to avoid theformation of cracks around the hole.

I have found that in the manufacture of cathode ray tubes the wholeprocess of punching a hole in the side wall of the bulb and sealing abutton contact in the hole can be carried out in about 1 minute, whilethe same procedure carried out with the conventional method of using gasfires requires at least 2 minutes. Comparatively little time is requiredto train operators to practice my invention with the aid of the fixtureshown in Fig. 1 and the seals produced are much more uniform inappearance and quality than those made by the conventional method usinggas fires.

I claim:

1. The method of perforating a sheet of glass which comprises placing aconcave metal punch with its edge in contact with the glass, heating theedge of the metal punch by induction to a temperature at which the glassadjoining said edge is softened, and pressing the heated punch throughthe softened glass.

2. The method of perforating a sheet of glass which comprises placing ametal punch having a concave end with the edge of said end in contactwith the glass, heating the edge of the metal punch inductively by ahigh frequency coil on the opposite side of the sheet and in registrywith said edge to a temperature at which the glass adjoining said edgeis softened, and pressing the heated punch through the softened glass.

3. The method of making a, circular hole in a sheet of glass whichcomprises placing a metal punch having an annular concave end with theedge of said end in contact with the glass, heating the edge of themetal punch by a single-turn high frequency coil of an inner diametergreater than said punch and coaxial with said punch to a temperature atwhich the glass adjoining said edge is softened, and pressing the punchwhile hot through the softened glass and through said coil.

4. The method of making a circular hole in the wall of the glass bulbwhich comprises placing a metal punch having a concave end with the edgeof said end in contact with the inner wall of said bulb, heating theedge of the metal punch by a single-turn high frequency coil on outsideof the bulb and coaxial with the edge of said punch to a temperature atwhich the glass adjoining said glass is softened, supporting the wall ofsaid bulb on an electrically non-conductive support having a hole largerthan said punch and coaxial with and surroundin said coil, and pressingsaid punch while hot through the softened glass.

5. Apparatus for perforating the wall of a glass bulb comprising a punchholder adapted to be inserted in a bulb, a concave metal punch adaptedto be mounted on said holder in position to engage the bulb wall, meansfor producing relative movement of said holder and said bulb to placethe concave punch with its edge against the bulb wall, and a highfrequency coil positioned outside the bulb and coaxial with said punchwhen said punch is in contact with the r bulb wall to heat by inductionthe edge of said punch.

6. Apparatus for perforating the wall of a glass bulb comprising a bulbcarrier adapted to be inserted in a bulb, a punch holder movably mountedon said carrier to move transversely of the wall of the bulb on saidcarrier, a concave metal punch loosely mounted on said holder, means formoving said holder to hold the edge of said punch against the inner wallof the bulb, and a high frequency single-turn coil of an inner diametergreater than the diameter of said punch positioned to be outside thewall of a bulb on said carrier and coaxial with the punch when saidpunch is in contact with the inner wall of said bulb.

7. Apparatus for perforating the wall of a glass bulb comprising anelongated bulb carrier adapted to be inserted in a bulb and mounted torotate about its longitudinal axis, an arm pivoted on said carrier toswing transversely of the axis of rotation of said carrier, actuatingmeans on said carrier for at will swinging said arm about its pivot, apunch holder on the free end of said arm, a concave metal punch adaptedto be loosely mounted on said punch holder, and a single-turn highfrequency induction coil of inner diameter greater than the outerdiameter of said punch and coaxial with said punch on said holder whensaid punch engages the Wall of a bulb on said carrier.

8. Apparatus for perforating the wall of a glass bulb comprising a bulbcarrier adapted to be inserted in a bulb, a punch holder mounted on saidcarrier to move transversely of said cater toward the wall of a glassbulb on said carrier, said holder comprising a punch support and a pinprojecting from said support in a direction of movement of said holder,a punch formed as a shallow metal cup having in its bottom a central.hole slightly larger than said pin, and a high frequency induction coilpositioned to heat by induction the edge of said punch on said ho de 9.The method of perforating an article of metallic fusible material, whichcomprises steps of causing a metal member to rest and 1 against asurface of the article, and creating in alternating electric field ofsuitable frequency about the member to cause the same to melt its waythrough the article.

10. Apparatus for perforatin the wall of a glass bulb comprising a metalpunch, a holder for said punch, said holder being mounted for relativemovement with respect to said bulb wall whereby said punch is placed incontact with wall, and means for creating an alternating clec tric fieldof suitable frequency about the punch to cause the same to melt its waythrough wall, said means being disposed outside of said bulb and incoaxial relation with respect to said punch.

11. Apparatus for perforating the wall of a glass bulb having an openingin registry with an axis thereof, comprising an elongated mem her havingan end portion adapted to be extended into said bulb through saidopening for ing inner wall portions of said bulb, an arm pivotallymounted on one end thereof on said end portion of said member forrotation on an axis transverse to the longitudinal axis of said memberwhereby said arm is adapted to swing to away from the wall of said bulb,a punch holder on the other end of said arm, a punch mounted on saidholder with its face opposite a wall portion of said bulb, said punchengaging said wall 8 portion in response to rotation of said arm, a highfrequency induction coil disposed outside of said bulb and adjacentthereto, and means for manually rotating said elongated member on itslongitudinal axis to dispose said punch in coaxial relation to saidcoil.

12. Apparatus for perforating the wall of a glass bulb comprising asingle turn high frequency coil, means for supporting said coil in ahorizontal plane, said coil comprising a support for said glass bulb, anelongated member adjustably supported to have one end extend into saidbulb, an arm pivotally mounted on said member adjacent the said one endthereof for rotation in a plane of said elongated member, a punch holdermounted on one end of said arm, a punch loosely mounted on said punchholder, means for rotating said arm for positioning said punch againstsaid glass bulb, and means for rotatin said elongated member on itslongitudinal axis for bringing said punch into registry with said coil.

13. The method of perforating an article of non-metallic fusiblematerial which comprises the steps of placing a metal punch in pressingcontact with a surface of said article and creating an alternatingelectric field of suitable frequency about the punch to heat the sameand cause it to melt its Way through the article.

14. The method of perforating a glass article which comprises the stepsof pressing the edge of a concave punch against a surface of saidarticle and heating said edge by induction to cause it to melt its waythrough said article.

15. The method of perforating an article of non-metallic fusibleinsulating material, which comprises the steps of pressing the edge of ametal concave punch against one surface of said article, and heatingsaid edge of said punch by a high frequency induction coil supportedagainst the opposite surface of said article to cause said edge to meltits way through said article.

GEORGE N. PHELPS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 810,474 Doane Jan. 23, 19061,722,010 Littleton et a1 July 23, 1929 2,374,706 Saslow May 1, 1945

